I’m not putting a download here as I don’t consider this finished just yet.

• The content pipeline only works with content in the serialized .xnb format.
• There are certain content types which can only be loaded via the content pipeline.
• Certain features don’t exist on the PC because they don’t exist on the XBox or Windows Phone 7.

Xna was designed as an abstraction layer for all the 3 platforms mentioned in the last point, so that one is somewhat understandable. I don’t want to write games for my XBox right now though, so why should things like drawing lines not be available to me?

With these points in mind I started working on Snowball. It’s designed to be an Xna like framework for making 2D games. It uses SlimDX on the backend, but that is completely abstracted away from consumers of the framework. What I want to do is design the API so that the backend can be swapped out somewhat painlessly.

I still have a ways to go before I will consider it a version 1.0 release. As of this writing, I’m transitioning to more of a ContentLoader class style for loading your game’s content. Any resource type from within the framework can be loaded by hand if you want, the ContentLoader class will just make it easier. After that I have a few other features like GamePad and Music which I would like to implement before saying I have a Beta type release.

The future after that is up in the air. I would love to try and have different implementations of the API for Xna and/or OpenTK.

I recommend for anyone who is interested as to why an API designer choose to implement the API in the way they did to try it for themselves. I have learned many things from this project including why certain design decisions were made by the Xna Framework team.

ManagementDateTimeConverter.ToDateTime(dmtfDate);

The format of Zune playlists is a simple XML format known as SMIL. I think Windows Media Player also stores playlists in this format but I haven’t confirmed that yet.

I wrote the tool very quickly and have only tested it on my machine with my test data, but I’ll provide the source if you’d like to modify for yourself. The source is C#.

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We’ll start by defining the Injectable attribute.

[AttributeUsage(AttributeTargets.Constructor | AttributeTargets.Property,
	AllowMultiple = false, Inherited = true)]
public class InjectableAttribute : Attribute
{
}

We’ll use this attribute to mark our constructors and properties for dependency injection. Next we’ll define an interface for our dependency injector:

public interface IDependencyInjector
{
	T Construct<T>();
	void Inject(object instance);
}

We’ll define our service container like so:

public class ServiceContainer : IDependencyInjector, IServiceProvider
{
	Dictionary<Type, Object> services;

	public ServiceContainer()
		: base()
	{
		this.services = new Dictionary<Type, object>();
	}

	public void AddService(Type type, Object provider)
	{
		if(null == type)
			throw new ArgumentNullException("type");

		if(null == provider)
			throw new ArgumentNullException("provider");

		if(this.services.ContainsKey(type))
			throw new InvalidOperationException("A provider is already registered the type " + type);

		var providerType = provider.GetType();

		if(!type.IsAssignableFrom(providerType))
			throw new InvalidOperationException(providerType + " is not an instance of " + type);

		this.services.Add(type, provider);
	}

	public object GetService(Type type)
	{
		if(null == type)
			throw new ArgumentNullException("type");

		if(this.services.ContainsKey(type))
			return this.services[type];

		return null;
	}

	public void RemoveService(Type type)
	{
		if(null == type)
			throw new ArgumentNullException("type");

		this.services.Remove(type);
	}

	protected object GetInjectableService(Type type)
	{
		if(type == typeof(IDependencyInjector) ||
		   type == typeof(IServiceProvider))
		{
			return this;
		}
		else
		{
			object service = this.GetService(type);

			if(service == null)
				throw new InvalidOperationException("Failed to find " + type + " depenedency.");

			return service;
		}
	}

	public T Construct<T>()
	{
		ConstructorInfo injectableConstructor = null;
		foreach(ConstructorInfo constructor in typeof(T).GetConstructors())
		{
			foreach(Attribute attribute in constructor.GetCustomAttributes(true))
			{
				if(attribute is InjectableAttribute)
				{
					injectableConstructor = constructor;
					break;
				}
			}

			if(injectableConstructor != null)
				break;
		}

		if(injectableConstructor == null)
			throw new InvalidOperationException("No injectable constructor found.");

		var parameters = injectableConstructor.GetParameters();
		var services = new object[parameters.Length];

		int i = 0;
		foreach(ParameterInfo parameter in parameters)
			services[i++] = GetInjectableService(parameter.ParameterType);

		return (T)injectableConstructor.Invoke(services);
	}

	public void Inject(object instance)
	{
		foreach(PropertyInfo property in instance.GetType().GetProperties())
		{
			foreach(Attribute attribute in property.GetCustomAttributes(true))
			{
				if(attribute is InjectableAttribute)
				{
					if(!property.CanWrite)
						throw new InvalidOperationException(property.Name + " is marked as Injectable but not writable.");

					property.SetValue(instance, GetInjectableService(property.PropertyType), null);
				}
			}
		}
	}
}

You can now construct new instances and inject dependencies on existing instances. Some usage examples:

public interface IFoo
{
	int Value { get; }
}

public class Foo : IFoo
{
	public int Value
	{
		get;
		set;
	}

	[Injectable]
	public Foo()
	{
	}

	public void DoIt()
	{
		Console.WriteLine(this.Value);
	}
}

public interface IBar
{
	string Value { get; }
}

public class Bar : IBar
{
	IFoo foo;

	public string Value
	{
		get;
		set;
	}

	[Injectable]
	public Bar(IFoo foo)
	{
		this.foo = foo;
	}

	public void DoIt()
	{
		Console.WriteLine(this.Value + ": " + this.foo.Value);
	}
}

public class Baz
{
	[Injectable]
	public IFoo Foo
	{
		get;
		set;
	}

	[Injectable]
	public IBar Bar
	{
		get;
		set;
	}

	public void DoIt()
	{
		Console.WriteLine(this.Bar.Value + " | " + this.Foo.Value);
	}
}

class Program
{
	static void Main(string[] args)
	{
		var container = new ServiceContainer();

		var foo = container.Construct<Foo>();
		foo.Value = 5;
		container.AddService(typeof(IFoo), foo);

		var bar = container.Construct<Bar>();
		container.AddService(typeof(IBar), bar);
		bar.Value = "Hello World!";
		bar.DoIt();

		var baz = new Baz();
		container.Inject(baz);
		baz.DoIt();
	}
}

I started by downloading and compiling the Windows API Code Pack in Release mode. I then added a reference to the Microsoft.WindowsAPICodePack.dll and Microsoft.WindowsAPICodePack.Shell.dll files to the project. After that add the lines:

using Microsoft.WindowsAPICodePack.Taskbar;

to your using statements. When the clock starts running I create the progress bar in the taskbar with:

// Initialize progress bar
if(TaskbarManager.IsPlatformSupported)
{
	TaskbarManager.Instance.SetProgressState(TaskbarProgressBarState.Normal);
	TaskbarManager.Instance.SetProgressValue(0, (int)this.totalTime.TotalSeconds, this.Handle);
}

to stop the progress bar:

// Stop progress bar
if(TaskbarManager.IsPlatformSupported)
	TaskbarManager.Instance.SetProgressState(TaskbarProgressBarState.NoProgress);

and finally to update the progress bar on each tick:

// Update progress bar
if(TaskbarManager.IsPlatformSupported)
	TaskbarManager.Instance.SetProgressValue((int)this.totalTime.TotalSeconds - (int)this.time.TotalSeconds, (int)this.totalTime.TotalSeconds, this.Handle);

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public static class SpriteBatchHelper
{
	static Texture2D pixel;

	private static void LoadPixel(GraphicsDevice graphicsDevice)
	{
		if(pixel == null)
		{
			pixel = new Texture2D(graphicsDevice, 1, 1);
			pixel.SetData<Color>(new Color[] { Color.White });
		}
	}

	public static void DrawRectangle(this SpriteBatch spriteBatch, Rectangle rectangle, Color color)
	{
		LoadPixel(spriteBatch.GraphicsDevice);
		spriteBatch.Draw(pixel, rectangle, color);
	}
}

For example, when you have interfaces in your library. You want to keep the number of methods in that interface as low as possible so that classes implementing the interface don’t have to do a lot of heavy lifting. This means cutting out methods in an interface that are for the most part just syntactic sugar for another method in the interface.

public interface IServiceContainer
{
    void AddService(Type type, Object provider);
    object GetService(Type type);
}

public static class IServiceContainerExtensions
{
    public static void AddService<T>(this IServiceContainer services, object provider)
    {
        services.AddService(typeof(T), provider);
    }

    public static T GetService<T>(this IServiceContainer services) where T : class
    {
        return services.GetService(typeof(T)) as T;
    }

    public static T GetRequiredService<T>(this IServiceContainer services) where T : class
    {
        T service = services.GetService(typeof(T)) as T;

        if(service == null)
            throw new ServiceNotFoundException(typeof(T));

        return service;
    }
}

All of the methods in IServiceContainerExtensions are just helper methods for method in IServiceContainer. By making them extension methods in our own library though, we’ve made the barrier to entry lower. Other people can implement the interface and in a sense “inherit” the helper methods as well.